The use of inks, coating compositions, coatings, or layers, containing magnetic or magnetizable pigment particles, in particular non-spherical optically variable magnetic or magnetizable pigment particles, for the production of security elements and security documents is known in the art.
Security features, e.g. for security documents, can be classified into “covert” and “overt” security features. The protection provided by covert security features relies on the concept that such features are hidden, typically requiring specialized equipment and knowledge for their detection, whereas “overt” security features are easily detectable with the unaided human senses, e.g. such features may be visible and/or detectable via the tactile senses while still being difficult to produce and/or to copy. However, the effectiveness of overt security features depends to a great extent on their easy recognition as a security feature, because users will only then actually perform a security check based on such security feature if they are aware of its existence and nature.
Coatings or layers comprising oriented magnetic or magnetizable pigment particles are disclosed for example in U.S. Pat. Nos. 2,570,856; 3,676,273; 3,791,864; 5,630,877 and 5,364,689. Magnetic or magnetizable pigment particles in coatings allow for the production of magnetically induced images, designs and/or patterns through the application of a corresponding magnetic field, causing a local orientation of the magnetic or magnetizable pigment particles in the unhardened coating, followed by hardening the latter. This results in specific optical effects, i.e. fixed magnetically induced images, designs or patterns which are highly resistant to counterfeit. The security elements based on oriented magnetic or magnetizable pigments particles can only be produced by having access to both the magnetic or magnetizable pigment particles or a corresponding ink or composition comprising said particles, and the particular technology employed to apply said ink or composition and to orient said pigment particles in the applied ink or composition.
Moving-ring effects have been developed as efficient security elements. Moving-ring effects consist of optically illusive images of objects such as funnels, cones, bowls, circles, ellipses, and hemispheres that appear to move in any x-y direction depending upon the angle of tilt of said optical effect layer. Methods for producing moving-ring effects are disclosed for example in EP 1 710 756 A1, U.S. Pat. No. 8,343,615, EP 2 306 222 A1, EP 2 325 677 A2, and US 2013/084411.
WO 2011/092502 A2 discloses an apparatus for producing moving-ring images displaying an apparently moving ring with changing viewing angle. The disclosed moving-ring images might be obtained or produced by using a device allowing the orientation of magnetic or magnetizable particles with the help of a magnetic field produced by the combination of a soft magnetizable sheet and a spherical magnet having its magnetic axis perpendicular to the plane of the coating layer and disposed below said soft magnetizable sheet.
The prior art moving ring images are generally produced by alignment of the magnetic or magnetizable particles according to the magnetic field of only one rotating or static magnet. Since the magnetic field lines of only one magnet generally bend relatively softly, i.e. have a low curvature, also the change in orientation of the magnetic or magnetizable particles is relatively soft over the surface of the OEL. Further, the intensity of the magnetic field decreases rapidly with increasing distance from the magnet when only a single magnet is used. This makes it difficult to obtain a highly dynamic and well-defined feature through orientation of the magnetic or magnetizable particles, and may result in visual effects that exhibit blurred ring edges.
WO 2014/108404 A2 discloses optical effect layers (OEL) comprising a plurality of magnetically oriented non-spherical magnetic or magnetizable particles, which are dispersed in a coating. The specific magnetic orientation pattern of the disclosed OELs provides a viewer the optical effect or impression of a loop-shaped body that moves upon tilting of the OEL. Moreover, WO 2014/108404 A2 discloses OELs further exhibiting an optical effect or impression of a protrusion within the loop-shaped body caused by a reflection zone in the central area surrounded by the loop-shaped body. The disclosed protrusion provides the impression of a three-dimensional object, such as a half-sphere, present in the central area surrounded by the loop-shape body.
WO 2014/108303 A1 discloses optical effect layers (OEL) comprising a plurality of magnetically oriented non-spherical magnetic or magnetizable particles, which are dispersed in a coating. The specific magnetic orientation pattern of the disclosed OELs provides a viewer the optical effect or impression of a plurality of nested loop-shaped bodies surrounding one common central area, wherein said bodies exhibit a viewing-angle dependent apparent motion. Moreover, WO 2014/108303 A1 discloses OELs further comprising a protrusion which is surrounded by the innermost loop-shaped body and partly fills the central area defined thereby. The disclosed protrusion provides the illusion of a three-dimensional object, such as a half-sphere, present in the central area.
A need remains for security features displaying an eye-catching bright loop-shaped effect on a substrate with good quality, wherein said security features can be easily verified, must be difficult to produce on a mass-scale with the equipment available to a counterfeiter, and which can be provided in great number of possible shapes and forms.